Sensory perception is vital for accurate hand movement, and learning is known to occur in both sensory and motor systems to keep movement accurate in a changing environment. Unfortunately, how the brain?s sensory and motor systems interact to achieve this is poorly understood. This knowledge gap limits advances in areas that depend on understanding the mechanisms underlying sensorimotor function. Existing roadblocks include: (i) Independent evolution of motor control and sensory perception research, where the importance of bridging these fields has only recently been recognized. (ii) Research that does bridge sensory and motor function typically deals with one sensory modality in isolation, rather than the natural multisensory state of the system. This makes it difficult to translate laboratory research to natural contexts. Hand position, for example, is perceived through both vision and proprioception (position sense, from the joints and muscles). (iii) Neuroimaging has identified human cortical regions active during simple multisensory stimuli but has rarely studied higher level multisensory processes such as visuo-proprioceptive realignment, one form of sensory learning related to spatial perception. To successfully shape multisensory-motor interactions in human behavior, the neural basis of complex multisensory processes must be understood. This project addresses all three roadblocks. The overall objective is to identify, in the context of visuo-proprioceptive processing, the roles of sensory vs. motor brain systems in sensory vs. motor learning. The central hypothesis is that sensory and motor brain areas interact reciprocally in hand control, with each having a role in both sensory and motor learning. Aim 1 will identify the role of sensory vs. motor brain areas in sensory vs. motor learning using transcranial magnetic stimulation (TMS), which transiently and focally reduces neural activity. In different groups of healthy participants, stimulation will be applied to brain regions traditionally considered unisensory, multisensory, or motor. Participants will then experience either: (Aim 1A) visuo-proprioceptive sensory learning; or (Aim 1B) motor learning. If learning is affected by TMS, a causal role for the stimulated brain region can be inferred. Using neuroimaging, Aim 2 will identify functional connections among unisensory, multisensory, and motor areas that change in association with visuo-proprioceptive realignment. This project is innovative in two ways: (i) It represents a shift from current research paradigms by studying brain regions traditionally considered unisensory, multisensory, and motor in a single set of experiments comprising multisensory vs. motor learning. (ii) The use of brain stimulation to infer the role of activity within brain areas, and neuroimaging to identify relevant connections between brain areas. The significance of the proposed research is that it will address the roadblocks to progress in the field by bridging sensory and motor research in a multisensory context and testing complex sensory and motor learning processes involved in natural human behavior.